1. Field of the Invention
The present invention relates to a time shift reproduction time controlling method for controlling time shift reproduction time and an information reproduction apparatus for controlling time shift reproduction time for use with a time shift reproduction system which can receive and temporarily record image data and sound data onto a recording medium and then reproduce an image and sound within predetermined time from the data recorded on the recording medium.
2. Description of the Related Art
Various reception apparatus which receive a digital television (digital TV) broadcast are available, and some of them have a time shift reproduction function which can temporarily record received encoded data onto a recording medium such as a hard disk (HD) and reproduce an image and sound from the encoded data recorded on the recording medium within time shift permitting time as a time limit. Use of the time shift reproduction function eliminates the necessity to effect reception of encoded data and reproduction of the encoded data simultaneously. Accordingly, even if a user temporarily leaves a reception apparatus in a situation wherein the user uses the reception apparatus to enjoy a TV program while the reception apparatus continues reception of encoded data, when the user subsequently returns to the location of the reception apparatus, the user can enjoy the TV program beginning with the contents of the TV program recorded at the point of time when the user left the reception apparatus. In other words, the reception apparatus can reproduce the program going back to the past by a fixed interval of time.
However, if the time within which it is permitted to record encoded data onto a recording medium is not limited, then the encoded data recorded on the recording medium may be re-utilized. For example, there is the possibility that the encoded data recorded on the recording medium may be transferred to and re-utilized on another apparatus such as a personal computer or may be provided from the user to and re-utilized by a third party. Since a provider of a TV program should originally receive an equivalent to re-utilization of its TV program, such re-utilization of encoded data of a user as described above spoils the benefit of the TV program provider, that is, the benefit based on the copyright.
Therefore, in order to limit the recording time of encoded data onto a recording medium, a limitation is provided to the storage region of a recording medium in a reception apparatus which has the time shift reproduction function. For example, such a countermeasure as to repetitively use a storage region for fixed time, that is, to overwrite the storage region with new encoded data for time exceeding the fixed time.
However, where the countermeasure is taken, encoded data within the storage region before overwritten with new encoded data can be stolen by successively transferring the encoded data to another storage area or to another recording medium. Although it becomes more and more significant to protect the copyright of a broadcasting program as popularization of the digital broadcasting proceeds, the countermeasure that the storage region for fixed time is repetitively used does not make a sufficient method for copyright protection.
Japanese Patent Laid-Open No. 2000-57059 discloses a system wherein, in order to prevent copying of encoded data of a broadcasting program or the like, the program providing side embeds time-of-day information into the encoded data using an electronic watermark technique and the reception apparatus side reproduces the time-of-day information and prevents reproduction of the encoded data at time of day after more than fixed time after the time-of-day indicated by the time-of-day information. With the system, however, if the time-of-day information is falsified, then reproduction of the encoded data is permitted at time of day after more than the fixed time after the time of day indicated by the time-of-day information.
Japanese Patent Laid-Open No. 2001-298719 discloses another system wherein the program providing side transmits transmission time-of-day information together with image data and the reception apparatus side reproduces the transmission time-of-day information and prevents reproduction of the image data at time of day after more than fixed time after the time of day indicated by the transmission time information. Also with the system just described, if the time-of-day information is falsified, then reproduction of the encoded data is permitted at time of day after more than the fixed time after the time of day indicated by the time-of-day information.